longbefore,beforelong,longbeforethen的意思,区别,用法?longbefore,beforelong,longbeforethen的意思,有什么区别,具体用法是什么?（请针对高中英语细说）

Question

long before ,before long,long before then的意思,区别,用法?
long before ,before long,long before then的意思,有什么区别,具体用法是什么?（请针对高中英语细说）

Answer 1

before long作“不久,很快”解,相当于soon,可用于过去时,也可用于将来时,而且只能单独作状语,后面不能接从句.如：
Before long he had to move on again．
不久,他只得再次搬迁.
I hope to see you again before long．
我希望不久可以见到你.
long before作“在……以前很久、很久以前”解,可接从句,这时before为连词；如：
Mark learned to read long before he started school.
马克上学之前很早就学会了看书.
The invention had been widely studied long before it was put to use.
这项发明在投入使用前进行了广泛研究.
也可什么都不接,这时before是副词.如：
He told me that he had seen the film long before．
他告诉我他早就看过这部电影了.